Reflecting diffraction gratings have been known for a long time. To improve their efficiency, or in other words their reflectively within an intended wavelength range (usually for the first order), the grooves are provided with a predetermined profile, that is a so-called blaze. The gratings are usually also provided with a metallized surface (for example, aluminum, gold, or platinum) on their front face, which is protected by an MgF.sub.2 layer as may be required. The reflectivity of the known gratings, despite the blaze and despite the metallizing, is markedly below 100%, often considerably below it. For many applications, in which maximally high intensity is important, this is a great disadvantage.
A method of producing diffraction gratings having an asymmetrical groove profile is known, for instance from German Pat. No. 2,118,674. A diffraction grating is also known from U.S. Pat. No. 4,475,792 which is mounted on the reflecting surface of an optical prism. This arrangement does increase the resolution by the factor n, where n is the index of refraction of the optical prism. However, it is disadvantageous that the reflectivity of this grating (even when it is metallized) is less than in conventional surface gratings, because the difference in the indices of refraction between metal and the optical material of the prism is less than that between metal and air. As a result, this known grating has even poorer efficiency than the normal reflecting diffraction grating.